The long-range objective is to characterize the mechanisms by which the function of retinal pericytes is altered under pathophysiological conditions. Pericytes, the cells which ensheathe the microvessels, are of interest since they appear to regulate the flow of blood within retinal capillaries. Also of interest is the fact that the selective loss of pericytes is one of the first histopathological findings in diabetic retinopathy. A premise of the project is that molecules in the microenvironment regulate the physiology of the pericyte. The investigators have focused on the consequences of a breakdown in the blood-retinal barrier since defects in this barrier occur commonly in important sight-threatening disorders such as diabetes. The research strategy is based on the premise that ion channels play a vital role in pericyte function. The investigators postulate that the activity of ion channels expressed by pericytes is altered when plasma-derived molecules leak from the vascular system at sites where the blood-retinal barrier is compromised. To address these issues, they have developed an experimental preparation in which the patch-clamp technique is used to analyze the activity of ion channels in pericytes located on micro- vessels freshly isolated from human and animal retinas. In preliminary studies, they discovered that plasma activates several types of ion channels in retinal pericytes. To clarify the mechanisms by which molecules from the vascular system regulate the function of pericytes, this project will address the following specific aims. (1) characterize the ion channels whose activities are altered when retinal pericytes are exposed to plasma; (2) test the hypothesis that insulin-like growth factor (IGF-1) is one of the plasma-derived molecules which regulates the function of ion channels in retinal pericytes; and (3) test the hypothesis that the activation of ion channels by plasma-derived molecules, such as IGF-1, is closely associated with an increase in the concentration of calcium within the pericyte. Over the long term, understanding the mechanisms by which pericytes respond to patho- physiological conditions will help in devising therapeutic strategies for maintaining the function and survival of pericytes in retinal disorders such as diabetic retinopathy.